Electroconductive coated paper and method of making the same



Dec. 5, 1961 L. H. SILVERNAIL ETAL 3,011,918

ELECTROCONDUCTIVE COATED PAPER AND METHOD OF MAKING THE SAME Filed May29, 1959 Coo/1h 9 0/ on e/ec/roco/youc/fl e Wo/gr dispers/b/e oo/ mer ofa v/ny/ben g/ ouo er'nory ammonium compound,

Paper Coo/m9 0/0/7 e/ec/roconouc/l've Wafer oAspersM/e polymer 0/0W'fly/bnjg/ qua/armory ammonium compound IN V EN TORS [Joya M Si/vernai/Mar/on W Z emo/ 147' 7' ORNE Y5 United States Patent O 3,011,918ELECTROCONDUCTIVE COATED PAPER AND METHOD OF MAKING THE SAME Lloyd H.Silvernail and Marion W. Zembal, Midland,

Mich., assignors to The Dow Chemical Company, Midland, Mich., acorporation of Delaware Filed May 29, 1959, Ser. No. 816,713 11 Claims.(Cl. 117-201) This invention relates to the manufacture of paper havinga printing surface containing an electroconductive material consistingof a polymer of a predominant amount of a vinylbenzyl quaternaryammonium compound and adapted to electrographic printing. It relatesmore particularly to paper having a printing surface adapted forelcctrographic printing and containing a polymer comprised of apolymerized vinylbenzyl quaternary ammonium compound, e.g. vinylbenzyltrimethyl ammonium chloride.

in the preparation of a coated paper it is common practice to prepare amixture of water and a pigment such as clay or the like, together withother materials suchas for example a soluble pyrophosphate which may actas a dispersing and stabilizing agent, and blend the mixture with anadhesive material to produce a composition useful in the art for coatinga cellulose web and produce a finished paper having a high degree ofbrightness, smoothness and gloss and a good finish and hand aftercalendering.

In the preparation of paper having a printing surface adapted forelectrographic printing it has previously been difiicult to find asatisfactory electroconductive substance which is favorably adapted forthe critical needs of good electroconductivity at low relative humidityand which is soluble or at least dispersible in aqueous media to form acoating composition that can readily be applied to paper or a celluloseweb in usual ways.

Among the requirements of a paper adapted for electrographic printing,it is necessary that the paper have a conductivity corresponding to avolume resistivity within the range of from 0.25 to 50 10 ohms atordinary temperatures and pressures, e.g. at room temperature andatmospheric pressure. The volume resistivity of paper is determined inusual ways, e.g. by measuring the surface resistivity of a sheet of thepaper between electrodes spaced 0.25 inch apart and extending 0.5 inchonto the surface from one edge of the paper. Since the surface of thepaper between the electrodes is relatively large compared to the volumeof the paper between the electrodes, and is substantially equal to thevolume, the determining of the surface resistivity can conveniently becarried out and is a measure of the volume resistivity of the paper. Theconductivity of the paper is the reciprocal of the resistivity. In otherwords, a paper adapted for electrographic printing and having aconductivity corresponding to a volume conductivity of from 4X10 to 0.0210- mho humidities of from 10 to 75 percent has correspondingly a volumeconductivity of from 4x10- 7 to 0.02 l() mho at said relativehumidities.

It has now been discovered in accordancewith the present invention thatpolymers of vinylbenzyl quaternary ammonium compounds can readily beincorporated with or applied as a coating to a cellulose web or paper toproduce a paper having an electroconductive surface adapted forelectrographic printing and possessing good electroconductivity at lowrelative humidity. It has further been found that a cellulose web orpaper containing polymers of vinylbenzyl quaternary ammonium compoundsis adapted for electrographic printing at relative humidities, betweenabout 5 and 100 percent and is advantageously employed for such printingat relative humidities of 25 percent or lower.

The polymers of vinylbenzyl quaternary ammonium compounds to be employedin practice of the invention can be any water-soluble orwater-dispersible homopolymer or copolymer of one or more vinylbenzylquaternary ammonium compounds, or copolymers of a predominant amount ofa vinylbenzyl quaternary ammonium compound and a minor amount of anonacidic copolymerizable compound such as acrylamide, or copolymerscontaining in the polymer molecules residues corresponding to from 95.0to 99.99 percent by weight of one or more vinylbenzyl qua-ternaryammonium compounds and from 5.0 to 0.01 percent by weight ofdivinylbenzene.

More specifically, the electroconductive substance can be a homopolymeror a copolymer of any two or more vinylbenzyl quaternary ammoniumcompounds having the general formula:

Y' RI! wherein R, R and R" each represents individually a monovalentradical selected from the group consisting of CH OHCH CH CHOHCH CHOHCHOHCH and alkyl, aryl cycloalkyl and aralkyl hydrocarbon radicals,and R, R and R collectively represent the trivalent radical of theformula:

CH-CH:

CH=CH wherein the three valences are attached to the nitrogen atom, thesaid R groups containing a total of not more than 12 carbon atoms in thesum of the constituent radicals, or a copolymer of at least 65 percentby weight of any one or more of such vinylbenzyl quaternary ammoniumcompounds with not more than 35 percent by weight of acrylamide, or acopolymer containing in the polymer molecules residues corresponding tofrom 95.0 to 99.99, preferably from 99.0 to 99.99, percent by weight ofany one or more of such vinylbenzyl quaternary ammonium compounds andfrom 5.0 to 0.01, preferably from 1.0 to 0.01, percent by weight ofdivinylbenzene. Mixtures of any two or more of the homopolymers orcopolymers can also be used. 7

The polymers are of relatively high molecular weight and arecharacterized by a viscosity of at least 2 centipoises for a 0.5 percentby weight solution of the polymer in an aqueous 2 percent by weightsolution of sodium chloride at 25 C. as determined with an Ostwaldviscosimeter. The term viscosity as herein employed refers to theviscosity of the aforesaid polymer solutions or dispersions under theabove conditions.

-In a preferred embodiment of the invention the electroconductivesubstance is a homopolymer or copolymer of one or more vinylbenzylquaternary ammonium cornponnds having the aforementioned general formulawherein R represents an alkyl radical containing from 1 to 4 carbonatoms, R and R" each represents a radical of the group consisting of OHOHCH CH CHOHOH OH OHCHOHCH and lower alkyl radicals containing from 1 to4 carbon atoms and Y is an anion, e.g. a sulfate, a chloride, a nitrate,or a hydroxyl ion, copolymers of at least percent by weight of any twoor more of such vinylbenzyl quaternary ammonium compounds andnot morethan 35 percent by weight of acrylarnide, or copolymers of from 99.0 to99.99 percent by weight of at least one such vinylbenzyl quaternaryammonium compound and from 1.0 to 0.01 percent by weight ofdivinylbenzene..

The vinylbenzyl quaternary ammonium compounds to be employed inpreparing the polymers for use in the invention can readily be preparedby reaction of vinylbenzyl chloride or bromide, (chloromethyDstyrene, or(bromomethyl)styrene, with a tertiary amine such as trimethylamine,triethylamine, tripropylamine, tributylamine, dimethylethanolamine,methyldiisopropanolamine, dimethylbenzylamine, dimethylaniline,dimethylcyclohexylamine, N,N dimethylarnino- 1,2 propanediol,triethanolam-ine, methyldiethanolamine and the like. The reaction of thevinylbenzyl halide and the tertiary amine proceeds readily attemperatures between about and 60 C., and can be carried out inadmixture with, or in the presence of, a solvent or reaction medium suchas water, ethyl alcohol,

' ethylene dichloride, toluene or the like, but a solvent is notrequired.

The vinylbenzyl quaternary ammonium compounds can be polymerized aloneor in admixture with one another, or in admixture with acrylamide ordivinylbenzene in the proportions previously stated to form thewater-soluble or Water-dispersible polymers suitable for use as theelectroconductive substance for use in the invention. The polymerizationcan be carried out in mass, i.e. in the substantial absence of an inertliquid medium, in solvents for the monomers or in a solvent for both themonomer and the polymer. Suitable solvents or polymerization media arewater, lower aliphatic alcohols such as methyl alcohol,'ethyl alcohol,isopropyl alcohol, or aliphatic ketones such as acetone or methyl ethylketone and mixtures of such compounds with water.

The, polymerization is accelerated by the use of polymerizationcatalysts such as heat, ultravioletlight, hydrogen peroxide, sodiumperborate, potassium persulfate, sodium persulfate, benzoyl peroxide,lauroyl peroxide, tertiary butyl peroxide, ditertiary butyl peroxide,tertiary butyl perbenzoate, cumene hydroperoxide or diisopropylbenzenehydroperoxide.

The polymerization of the monomers can be carried out at temperaturesbetween 0 and 100 C. and at atmospheric, subatmospheric or superatmospheric pressures, but

in all cases is carried out at temperatures below the decompositiontemperature of the monomeric material and at pressures 'suflicient tomaintain the monomers in a liquid condition.

In preparing paper having a printing surface containing theelectroconductive polymers, the polymer can be incorporated on or withthe cellulose web or paper by coating, dipping, brushing, calendering orother usual ways of applying a solution or dispersion of the polymer,preferably an aqueous solution or dispersion of the polymer, to thepaper and thereafter drying the same to produce a final productcontaining the electroconductive polymer in Testing Methods, RecommendedPractices, Specifications, by the Technical Association of the Pulp andPaper Industry.

EXAMPLE 1 In each of a series of experiments, a sheet of 51 pounds perream of bleached sulfite base paper, sized on one side, was coated onthe sized side with a layer of an aqueous solution containing 20 percentby weight of a homopolymer of vinylbenzyl trimethyl ammonium chloride,then was dried in an air oven at 220 F. for a period of 2 minutes andWeighed. The paper contained a coating of the homopolymer correspondingto 1.4 pounds of the homopolymer per 1000 square feet of the coatedpaper. The homopolymer of vinylbenzyl trimethyl ammonium chlorideemployed in the experiment had a molecular weight corresponding to aviscosity characteristic of 1.63 centipoises as determined for a 0.5weight percent solution of the homopolymer in an aqueous 2 weightpercent solution of sodium chloride at C. Test pieces were cut from thepolymer coated paper. These test pieces were conditioned in air having arelative humidity as stated in the following table, at a temperature of75 C. for a period of 24 hours, then were tested for surface resistivityemploying a procedure similar to that described in AS'IlM D257-46. Tablel identifies the experiments and gives the surface resistivity expressedas ohms of the polymer coated paper at the stated relative humidity. Thecoated paper had a printing surface adapted for electrographic printing.

In each of a series of experiments, a sheet of 51 pounds per ream ofbleached sulfite base paper, sized on one the desired amount; Theproportion of the electroconduc I tive polymer can be varied in amountcorresponding to from about 0.5 to 5 pounds of the polymer per 1000square 7 feet of the paper. The amount of the polymer to be incorporatedwith the paper can bevar-ied by'change in the concentration of thepolymer in the aqueous solution or dispersion employed for the coatingor dipping operation.

The electroconductive polymer is preferably applied to the paper orcellulose web as a surface coating or by dipping of the paper in anaqueous solution or dispersion of the polymer, after which the treatedpaper is driedin usual ways, e.g.by calendering or man oven.

I I 7 FIG. 1 of the drawing is an enlarged view of a section of paperhaving on one side a continuous coating ofan electroconductivewater-dispersible polymer prepared in face adapted for electrographicprinting.

. The following examples illustrate ways in which the principle of theinvention has been applied, but are not to be construed as limiting itsscope. In the examples, pro- "cedures identified by the designationTAPPi refer to standard methods published in Tentative and OfiicialExample1. Table II identifies the experiments and gives the weight ofthe polymer coating expressed as pounds side, was coated with a layer ofan aqueous solution of a homopolymer of vinylbenzyl trimethyl ammoniumchloride similar to that employed inExample 1, then was dried to obtaina paper having a coating of the homo polymer in amount as stated in thefollowing table. Test pieces'were cut from the coated sheet and weretested for surface resistivity at relative humidities as stated in thetable employing procedure similarto that employed in of the polymer per1000 squarefeet of the coated paper.

trographic printing.

Table II Polymer Relative Surface Run No. Coating, Humidity,Resistivity,

y lbs/1.000 Percent ohmsXlO sq. ft.

EXAMPLE 3 In each of a series of experiments, a sheet of 51 pounds perream of bleached sulfite base paper, sized on one side, was coated bydipping it in an aqueous solution of a homopolymer of vinylbenzyltrimethyl ammonium chloride similar to that employed in Example 2, whichsolution contained the homopolymer in a concentration of percent byweight. The dipped paper was passed between squeeze rolls, then wasdried in an air oven at 220 F. and was weighed to determine the percentby weight of the homopolymer incorporated in the paper. Test pieces ofthe impregnated paper were used to de termine the surface resistivity atrelative humidities as stated in the following table.

Table III Relative Humidity, Percent Polymer Coating on Paper, PercentSurface Run No. Re-

sistivity,

EXAMPLE 4 In each of a series of experiments, a sheet of 51 pounds perream of bleached sulfite paper, on one side, was coated with a layer ofan aqueous solution of a homopolymer of vinylbenzyl trimethyl ammoniumchloride, which homopolymer had a molecular weight corresponding to aviscosity characteristic of 1.63 centipoises as determined for a 0.5weight percent solution of the homopolymer in an aqueous 2 weightpercent solution of sodium chloride at C., then was dried in an air ovenat a temperature of 220 F. to obtain a coated paper containing an amountof the homopolymer as stated in the following table. Test pieces werecut from the coated paper and were conditioned in air at a relativehumidity as stated in the table at 75 C. for a period of 24 hours, thenwere tested for surface resistivity employing a procedure similar tothat described in ASTM D257-46. Table IV identifies the experiments andgives the proportion of the homo polymer expressed as percent by weightof the coated paper. The table also gives the surface resistivity of thecoated paper.

Table IV Surface Resistivity at Humidity of Homopolymer, Percent 10percent,

20 percent, ohmsXlO 55 percent, ohms l0 76 percent, 0hms 10 EXAMPLE 5 Ineach of a series of experiments, a sheet of 51 pounds per ream ofbleached sulfite paper, sized on one side, was coated by dipping it inan aqueous solution of a homopolymer of vinylbenzyl trimethyl ammoniumchlo- Table V Homo- Surface Resistivity at relative humidity of Runpolymer, No. lbs/1,000

sq. ft. 10 percent, 20 percent, 55 percent, 76 percent, ohms 10 ohn1s 10ohms 10 0hrns 10 EXAMPLE 6 (A) A water-dispersible copolymer containingin the polymer molecules residues corresponding to vinylbenzyl trimethylammonium chloride cross-linked with about one percent by weight ofdivinylbenzene was prepared by polymerizing a mixture of 99 percent byweight of vinylbenzyl chloride and 1 percent of divinylbenzene in anaqueous emulsion employing the recipe:

Ingredients: Parts by weight Monomers 100 Water Triton 200 (28 percentliquid solution of sodium salt of alkyl aryl polyether sulfate) 14Potassium persulfate 0.5

The ingredients were placed in a sealed vessel and were agitated andmaintained at a temperature of 30 C. for a period of 16 hours. Acoagulum-free latex was obtained in quantitative conversion of themonomers to copolymer. The latex was diluted with six times its weightof water and was mixed with 182 grams of an aqueous 25 weight percentsolution of trimethylamine. The resulting mixture was stirred andmaintained at 2530 C. for a period of 2 hours. A transparent viscoussolution of the copolymer containing residues corresponding tovinylbenzyl trimethyl ammonium chloride cross-linked with thedivinylbenzene was obtained.

(B) In each of a series of experiments, a sheet of 51 pounds per ream ofbleached sulfite paper, sized on one side, was coated with a layer ofthe solution of the copolymer prepared in part (A) above, then was driedin an air oven at a temperature of 220 F. The dried paper contained 1.1pounds of the copolymer per 1000 square feet of the paper. Test piecesof the coated paper were conditioned in air at a relative humidity asstated in the following table at 75 C. for 24 hours, then were testedfor surface resistivity. The results were as follows:

Surface resistivity,

Relative humidity, percent: ohmsx 10 EXAMPLE 7 Surface resistivity,

Relative humidity, percent: ohms 10 7 EXAMPLE 8 Surface resistivity,

Relative humidity, percent: ohms EXAMPLE 9 A sheet of 51 pounds per reamof bleached sulfite paper was coated with a layer of an aqueous solutionof a homopolymer corresponding to polymerized vinylbenzyl trimethylammonium chloride, which polymer was prepared by polymerizingvinylbenzyl chloride in an aqueous emulsion in the presence of 0.1percent by weight of dodecyl mercaptan and reacting the polymer with thetrimethylamine, employing procedure similar to that described in part(A) of Example 6. The paper was coated and tested employing proceduressimilar to those employed in part (B) of Example 6. The coated papercontained the copolymer in amount corresponding to one pound of thecopolymer per 1000 square feet of the paper. It had a surfaceresistivity as follows:

Surface resistivity,

Relative humidity, percent: ohms X 10 Similar results are obtained whenthe polymer is incorporated with the paper by dipping the paper in theaqueous solution and thereafter drying the paper.

We claim:

1. A paper having a printing surface adapted for electrographic printingand containing on said surface a continuous coating of anelectroconductive water-dispersible polymer consisting of at least onemember of the group consisting of (a) homopolymers of a vinylbenzylquaternary ammonium compound having the general formula:

. H2C=CELCoHrCHz-N-Rf wherein R, R" and R" each represents individuallya cals, (b) copolymers of at least two. of such vinylbenzyl quaternaryammonium compounds, (0) copolymers of at least 65 percent by weight ofat least one of suchvinylbenzyl quaternary ammonium compounds and notmore than. 35 percent by weight of acrylamide, and(d) corpolymers.corresponding to.fr0m.95.0to 99.99 percent by weight of. at least.oneof. such vinylbenzyl quaternary ammonium compounds and from 5.0m.0.01 percent by 8 weight of divinylbenzene, said electroconductivewaterdispersible polymer being present in amounts corresponding to from0.5 to 5 pounds of the polymer per 1000 square feet of the paper.

2. A paper having a printing surface adapted for electrographic printingand containing on said surface a continuous coating of anelectroconductive water-dispersible polymer consisting of at least onehomopolymer of a vinylbenzyl quaternary ammonium compound having thegeneral formula:

R H2c=oH-oaH,-cH2NR' RI wherein R, R and R" each represents individuallya monovalent radical selected from the group consisting of" I CH=CH-wherein the three valences are attached to the nitrogen atoms, and Y isan anion, said R groups containing a' total of not more than 12 carbonatoms in the substituent radicals, said electroconductivewater-dispersible polymer being present in amount corresponding to from0.5 to 5 pounds of the polymer per 1000 square feet of the paper.

3. A paper having a printing surface adapted for electrographic printingand containing on said surface a continuous coating of anelectroconductive water-dispersible polymer consisting of a copolymer ofat least 65 percent by Weight of a vinylbenzyl quaternary ammoniumcompound having the general formula:

H O=CH-O H -CH;NR'

Y R wherein R, R and R each represents individually a monovalent radicalselected from the group consisting of CH 0H'CHOHCH and alkyl, aryl,cycloalkyl and aralkyl hydrocarbon radicals, and R, R and R"collectively represent the trivalent radical of the formula:

wherein the three valences are attached to the nitrogen atom, and Y isan anion, said R groups containing a total of not more than 12 carbonatoms in the substituent I .radicals, and not more than 35 percent ofac-rylarnide,

said polymer being present iriamount corresponding to from 0.5 to 5pounds of the polymer per 1000 square feet of the paper.

4.. A paperhaving a. printing surface adapted for electrographicprinting and containing on said surface a continuous coating of anelectroconductive water-dispersible polymer corresponding to a copolymerconsisting of from 95.0 to 99.99 percent by Weight of avinyl-benzylquaternary ammonium compound having the general formula:

. wherein R, Rand R each represents individually a V I CH OH- CH O H CI-I-- and alkyl, aryl,cycloalky1 and 9 aralkyl hydrocarbon radicals, andR, R and R" collectively represent the trivalent radical of the formula:

wherein the three valences are attached to the nitrogen atom and Y is ananion, said R groups containing a total of not more than 12 carbon atomsin the substituent radicals, and from 5.0 to 0.01 percent ofdivinyl-benzene, said polymer being present in amount corresponding tofrom 0.5 to pounds of the polymer per 1000 square feet of the paper.

5. A method of making a paper having a printing surface containing anelectroconductive water-dispersible polymer and which paper is adaptedfor electrographic printing, which method comprises contacting at leastone of the major surfaces of the paper with an aqueous solution of awater-dispersible polymer selected from the group consisting of (a)homopolymers of a vinylbenzyl quaternary ammonium compound having thegeneral formula:

tively represent the trivalent radical of the formula:

CH-CH:

oH=0H- wherein the three valences are attached to the nitrogen atom, andY is an anion, said R group containing a total of not more than 12carbon atoms in the substituent radicals, (b) copolymers of at least twoof such vinylbenzyl quaternary ammonium compounds; (0) copolymers of atleast percent by weight of at least one of such vinylbenzyl quaternaryammonium compounds and not more than 35 percent of acrylamide, and (d)copolymers corresponding to from 95.0 to 99.99 percent by weight of atleast one of such vinylbenzyl quaternary ammonium compounds and from 5.0to 0.01 percent of divinylbenzene, and drying said paper, whereby saiddried paper contains said polymer on the printing surfact in the form ofa continuous coating in amount corresponding to from 0.5 to 5 pounds ofthe polymer per 1000 square feet of the paper.

6. A method as claimed in claim 5, wherein the waterdispersible polymeris a homopolymer of a vinylbenyl quaternary ammonium compound of group(a).

7. A method as claimed in claim 6, wherein the waterdispersible polymeris a homopolymer of vinylbenzyl trimethyl ammonium chloride.

8. A method as claimed in claim 5, wherein the waterdispersible polymeris a copolymer of at least 65 percent by weight of at least onevinylbenzyl quaternary ammonium compound of group (a) and not more than35 percent of acrylamide.

9. A method as claimed in claim 8, wherein the waterdispersible polymeris a copolymer of vinylbenzyl trimethyl ammonium chloride andacrylamide.

10. A method as claimed in claim 5, wherein the waterdispersible polymeris a copolymer of from 95.0 to 99.99 percent by weight of at least onevinylbenzyl quaternary ammonium compound of group (a) and from 5.0 to0.01 percent by weight of divinylbenzene.

11. A method as claimed in claim 10, wherein the water-dispersiblepolymer is a copolymer of vinylbenzyl trimethyl ammonium chloride anddivinylbenzene.

Morris Nov. 27, 1956 Wilson et al Apr. 28, 1959 UNITED STATES PATENTOFFICE CERTIFICATION OF CORRECTION Lloyd H. Silvernail et a1.

he above numbered petthat error appears in t Patent should read as It ishereby certified that the said Letters ent requiring correction andcorrected below.

23 to 26, the formula should appear as Column 8. lines f as in thepatent:

shown below instead 0 CHCH= column 9 line 30, for "CH CHOH -CH read CH-CHOHCH column lO lines 10 and 11, for I "surfact" read surface line l5for "'vinylbenyl read vinylbenzyl line 39 under "References Cited"strike out "2,772,310 Morris Nov. 27 1956",

Signed and sealed this. 26th day of June I962 (SEAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of PatentsDecember 5, 1961 Patent No. 3,011,918

Lloyd H. Silvernail et al.,

ertified that error appears in the above numbered pat- Patent shouldread as It is hereby c n and that the said Letters ent requiringcorrectio corrected below.

Column 8, lines 23 to 26 the formula should appear as shown belowinstead of as in the patent:

CHCH= column 9 line 30, for "CH CHOH CH read CH =-CHOH-CH "-3 11 for"surfact" read surface column 10 lines 10 and line 15 for "vinylbenyl"read vinylbenzyl line 39 under "References Cited" strike out 2,772,310Morris -=-Nov. 2'7 1956",

Signed and sealed this 26th day of June (SEAL) Attest:

DAVID L. LADD ERNEST W. SWIDER Attesting Officer Commissioner of Patents

5. A METHOD OF MAKING A PAPER HAVING A PRINTING SURFACE CONTAINING ANELECTROCONDUCTIVE WATER-DISPERSIBLE POLYMER AND WHICH PAPER IS ADAPTEDFOR ELECTROGRAPHIC PRINTING, WHICH METHOD COMPRISES CONTACTING AT LEASTONE OF THE MAJOR SURFACES OF THE PAPER WITH AN AQUEOUS SOLUTION OF AWATER-DISPERSIBLE POLYMER SELECTED FROM THE GROUP CONSISTING OF (A)HOMOPOLYMERS OF A VINYLBENZYL QUATERNARY AMMONIUM COMPOUND HAVING THEGENERAL FORMULA: